1. Field of the Invention
This invention relates to a horizontal deflection output circuit for a picture tube, having a damper diode.
2. Description of the Prior Art
"Transistor Circuit Design Manual", pp. 297-302, published by Ohm Co., Tokyo, Japan, discloses a horizontal deflection output circuit in which a resonance capacitor, a horizontal output transistor and a damper diode are respectively connected in parallel with the horizontal deflection coil for a picture tube, whereby the horizontal deflection current flows through the damper diode from the beginning of the horizontal scanning period to a certain intervening instant during the period and through the horizontal output transistor from the intervening instant to the end of the horizontal scanning period while a resonant current flows through the resonance capacitor during the horizontal flyback period. Like kindred semiconductor diodes having their characteristics cut-off frequencies, the damper diode used in the well-known circuit is not free from a limitation due to its cut-off frequency and therefore its transition from the cut-off state to the conductive state never takes place instantaneously but proceeds gradually over a very short period of time, the short period being usually called a rise time. Accordingly, during the rise time, which immediately follows the start of the horizontal scanning period, the deflection current is deficient and moreover the parasitic oscillation current due to the higher harmonics contained in a flyback pulse is superimposed on the deflection current, so that the linearity of the deflection current is degraded during the rise time. Moreover, the electron beam is velocity-modulated by the parasitic oscillation component superimposed on the deflection current. This causes an undesirable variation in brightness of the reproduced picture immediately after start of the horizontal scanning period. This undesirable phenomenon brings about no specific problem in the case of an ordinary television receiver in which over-scanning is employed since the phenomenon occurring immediately after the start of the horizontal scanning period is not reproduced in that region of the picture screen which is to be seen by watchers. In the case, however, where the whole information over the entire scanning period is always reproduced in the effective region of the picture screen, some vertical strips appear near the right or left hand side of the picture screen. Further, if higher harmonic components due to the parasitic oscillation leaks into the high frequency circuit, black vertical stripes appear near the right or left hand side of the picture screen.